It is known in the prior art to use so called shape memory alloys such as Nitinol in a thermobile engine. Such an engine is described in the article "The Thermobile Nitinol Engine" by Frederick E. Wang, Society of Automotive Engineers Inc., 1985, which article is incorporated in this application by reference. Nitinol is a nickel-titanium alloy having memorization properties.
A wire of a shape memory alloy can easily be deformed to any shape. However, when the wire is heated above a certain transition temperature, it assumes a rigidity and preset configuration. The transition temperature is determined by the composition of the alloy.
The driving device according to the above mentioned article consists of a wire loop of a shape memory alloy drivingly engaging two wheels having dissimilar diameters. The wire is heated above the transition temperature at the smaller wheel, thereby causing the wire to assume a straight shape and the wheel to rotate. The wire is then cooled below the transition temperature on its travel to the larger wheel. The thermobile, according to the referenced article, uses air as the cooling medium for the wire and some form of heat energy, such as hot water, for the heating medium. The disadvantage with a driving device of this kind is that the efficiency of cooling is low and therefore the RPM value is low.